Motivated by tensegrity as model of cell mechanical behavior, the goal of this application is to provide evidence that prestress in the actin cytoskeleton (CSK) is the primary determinant of a cell's resistance to shape change. The investigators hypothesize that the prestress is partly balanced by the extracellular matrix and partly by compressive elements of the CSK. Prestress will be inferred from the strain distributions imposed by adherent human airway smooth muscle cells (HASM) on deformable polyacrylamide gel substrates and related to magnetic twisting cytometry derived estimates of cell deformability. The investigators will test specific quantitative predictions most notably that: 1) the static shear modulus, a mechanical index of cell deformability, increases with increasing prestress; and 2) that microtubules are compression elements of the CSK which balance a substantial part of the prestress. The prestress will be modulated pharmacologically and by modulating cell spreading. The role of prestress on dynamic cell behavior will be evaluated and tested against the prediction that the cell mechanical impedance can be represented as a product of two terms: one which is strictly frequency dependent and represents the rheologic properties of CSK filaments and the other which depends on the prestress, but not on frequency. An energetic approach will be used to determine the relative contributions of various CSK structures and the extracellular matrix to the energy budget of the cell.